Films and tapes

DETAILED DESCRIPTION We claim: 1.
A method of producing a film or tape characterised in that a blend of from 30 to 70 parts by weight of a first thermoplastic fibre-forming polymeric component and from 70 to 30 parts by weight of a second, immiscible, thermoplastic fibre-forming polymeric component is spun into a film or tape wherein each component is present in the film or tape as fibrils which are substantially aligned to the longitudinal axis of the film or tape, such aligned fibrils of one polymeric component being interconnected to each other in a random manner, such interconnections penetrating through the fibrils of the other polymeric component such that both components exist in the film or tape as interpenetrating networks and then, using a solvent for the second polymeric component, leaching away from the film or tape the second fibre-forming polymer leaving a low density, porous film or tape of the first fibre-forming polymer.
2.
A melt spun film or tape produced by the method of claim 1.
3.
A filtration or separation medium comprising a film or tape produced by the method of claim 1.




Description:
This invention relates to melt spun films and tapes of a thermoplastic fibre-forming polymer.
According to the present invention we provide a melt spun film or tape of a thermoplastic fibre-forming polymer comprising spaced fibrils of the polymer which are substantially aligned to the longitudinal axis of the film, such aligned, spaced fibrils being interconnected to each other in a random manner.
We have found that a film or tape can be produced by forming a blend of the polymer and another thermoplastic, film-forming polymer by melt spinning the blend and then leaching away the other polymer using a suitable solvent leaving a low density, porous, film or tape according to the invention.
The structure of the blend at spinning was determined by examination of the extrudate upon exit from the spinneret.
This was sectioned and examined under the microscope.
Usually melt blends of two immiscible polymers produce a two phase system where one polymer forms the continuous phase and the other the discontinuous phase, which appears as globules in the extrudate